How should I practice Parse Query String?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Airbnb phone screen problems in FastPrep.

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Problem · String

Parse Query String

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Problem statement

Given a GET request query string, parse the key-value pairs into a normalized string serialization.

The input may start with ?. Parameters are separated by &. A parameter has one of the following forms:

key=value stores the parsed value for key.
!key stores the boolean value true for key. The prefix must appear at the start of a parameter. The forms !!key and !key=value are invalid.

Keys may repeat. Preserve all values in insertion order.

Value types

Integer: a sequence of digits.
Boolean: true or false.
Quoted string: remove the surrounding double quotes.
List literal: expand [item1,item2,...] into separate values in order.

Practice rule: An empty list [] still creates the key but adds no values. If that key receives no other values, serialize it as key=.

Return one entry per distinct key in first-appearance order. Use key=value for one value and key=value1|value2|... for multiple values.

Function

parseQueryString(query: String) → String[]

Examples

Example 1

query = "?key1=1&key1=\"abc\"&key2=value1&!isBooleanField"return = ["key1=1|abc","key2=value1","isBooleanField=true"]

key1 appears twice, so both values are preserved. The boolean shorthand !isBooleanField stores true.

Example 2

query = "page=2&active=false&tags=[red,blue]&page=3"return = ["page=2|3","active=false","tags=red|blue"]

The list literal [red,blue] expands into two separate values red and blue for the key tags. Because page appears twice (values 2 and 3), its entry uses the pipe-separated multi-value format. Keys are ordered by first appearance: page, active, tags.

Constraints

0 <= query.length <= 10⁵
Keys are non-empty and contain only letters, digits, underscores, or hyphens.
Values do not contain unescaped &.
The !key boolean shorthand appears only as a standalone parameter (i.e., the parameter contains no = sign and the key is prefixed with exactly one !).
List literal items are separated by commas with no whitespace; items are plain strings (not quoted).
Inputs are well-formed; invalid forms such as !!key, !key=value, or nested list literals do not appear.